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Magnetically biased tilting roller bearing tape guidance

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Magnetically biased tilting roller bearing tape guidance


A tape movement constraint for a tape drive system, comprises a tiltable tape roller bearing having a grooved surface adapted to contact and engage a surface of the tape as the roller barrel rotates, and an actuator adapted to pivot the roller bearing surface when the actuator is actuated, to control the lateral position of a tape. In operation, in one embodiment, a roller barrel of the tiltable roller bearing is biased in a first position on a pivot axis, using magnetic attraction between a movable magnet and a return path structure of magnetically permeable material. The roller barrel is pivoted on the pivot axis by conducting current through a fixed coil to generate a magnetic field which is conducted by the return path structure to interact with the magnetic field of the magnet. Other embodiments are described and claimed.
Related Terms: Magnetic Field

Browse recent International Business Machines Corporation patents - Armonk, NY, US
USPTO Applicaton #: #20130021693 - Class: 360 7304 (USPTO) - 01/24/13 - Class 360 


Inventors: Armando Jesus Argumedo, Nhan Xuan Bui, William Marvin Dyer, Reed Alan Hancock, David Howard Flores Harper, Wayne Isami Imaino, Kevin Bruce Judd

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The Patent Description & Claims data below is from USPTO Patent Application 20130021693, Magnetically biased tilting roller bearing tape guidance.

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FIELD

This description relates to tape drive systems for moving a tape, such as a recording tape for storing information, longitudinally across a head where the tape is subject to lateral movement.

BACKGROUND

Typically, tape drive systems provide tape guides for controlling the lateral movement of the tape as the tape is moved along a tape path in a longitudinal direction across a tape head. The tape may have a plurality of data tracks extending in the longitudinal direction, and the tape drive system may provide a track following servo system for moving the tape head in a lateral direction for following lateral movement of the longitudinal tracks as the tape is moved in the longitudinal direction. The track following servo system may employ servo tracks on the tape which are parallel to the data tracks, and employ servo read heads to read the servo tracks to detect position error and thereby position the tape head at the data tracks and follow the data tracks. This allows the data tracks to be placed closely together and increase the number of data tracks.

The tape is typically contained in a cartridge of one or two reels, and the tape is moved between a supply reel and a take up reel. The reels typically have runout causing the tape to move laterally as the tape is moved longitudinally. Tape guides can to an extent limit at least the amplitude of the lateral movement of the tape with the goal of limiting the lateral movement so that it does not exceed the lateral movement capability of the track following servo system.

In functions other than tape guiding, such as a tension roller (U.S. Pat. No. 4,310,863), an inertia roller (U.S. Pat. No. 4,633,347), or a tape timer roller (U.S. Pat. No. 3,037,290), where only longitudinal motion of the tape is concerned, high friction rollers that are in the tape path and displaced a considerable distance from the tape head, are intended to prevent or reduce tape slippage longitudinally with respect to the roller.

Typical tape guides may comprise stationary buttons or edges, or flanges at the side of tape guide rollers, positioned against the edges of the tape to control the amplitude of the lateral movement of the tape. In order to increase the total capacity of a tape, the tape is increasingly made thinner to allow more wraps of tape to fit on a given tape reel. As a result, the tape can be relatively weak in the lateral direction, and can, in some instances, be relatively easily damaged at the edge from the tape guide. Thus, the tape guides are typically positioned at a bearing where the tape assumes a cylindrical shape, thus increasing the ability of the tape edge to support a load. The tape roller bearing is generally rotatable about a central axis parallel to the cylindrical peripheral surface, allowing the tape freedom of movement in the longitudinal direction.

The bearing is also typically designed to have low friction. This arrangement can minimize the potential to distort the edge of the tape as the guides push against the edges of the tape to move the tape to the center of the bearing to reduce the amplitude of lateral displacement of the tape. One example is illustrated in U.S. Pat. No. 5,447,279, which employs an air bearing to reduce the friction of the bearing for stationary tape guides. One type of bearing in which the tape engagement surface remains stationary may also be referred to as a fixed pin or post. Other bearings such as roller bearings may have rotating tape engagement surfaces which reduce the longitudinal friction of the bearing while the flanges of the roller bearings push against the edges of the tape. One example of a roller bearing or fixed pin with flanges arranged to have low friction is U.S. Pat. No. 4,427,166. Fixed surfaces may also be arranged to have low friction. One example is described in U.S. Pat. No. 4,466,582, where a synthetic resin or metal coated tape guide bearing has a reduced contact area for the tape to lower the friction between the guide surface and the running tape and allow the flanges to stabilize the tape.

However, when wound on a reel, tape is typically subjected to stack shifts or stagger wraps, in which one wrap of the tape is substantially offset with respect to an adjacent wrap. Thus, as the tape is unwound from the reel, there can be a rapid lateral transient shift of the tape. Other common sources of rapid lateral transient shifts include 1) a buckled tape edge in which the tape crawls against a tape guide flange and suddenly shifts laterally back down onto the bearing, 2) a damaged edge of the tape which causes the tape to jump laterally when contacting a tape guide, and 3) when the take up reel or supply reel runout is so significant that the reel flange hits the edge of the tape.

Because of the low friction of the bearing and the low mass of the tape, rapid lateral transient shift of the tape at any point of the tape path may not be slowed by the typical tape guide and thus may be transmitted along the tape path to the tape head.

A tape head track following servo system may comprise a single actuator, or a compound, multiple element actuator. The transient response of the tape head track following servo system typically comprises a high bandwidth for a very limited lateral movement, called “fine” track following, to permit the tape head to follow small, relatively rapid displacements of the tape. Larger movement of the tape head is typically conducted as “coarse” track following, which is also employed to shift the tape head from one set of tracks to another set, and is typically conducted at a slow rate. The occurrence of a lateral transient shift, however, can be so rapid that neither the fine track follower nor the coarse track follower is able to respond, with the result that the tracking error becomes so large that writing may be stopped to prevent overwriting an adjacent track and to insure that the tracking error on read back is not so large as to cause a readback error.

One approach has been to make the tape guide edges or flanges closer together to maintain a pressure on both edges of the tape. However, this tends to stress and damage the edges of the tape, reducing its durability. An attempt at reducing the stress comprises spring loaded tape guides, such as the above-mentioned \'279 patent. However, although the amplitude of the tape shift may be reduced somewhat by this approach, the speed of the shift is typically not reduced, and a track following servo error may still occur, reducing the performance of the tape drive.

U.S. Pat. No. 6,754,033 describes a tape roller bearing having a cylindrical peripheral surface comprising a grooved frictional surface for contacting and engaging the surface of the tape, allowing the tape to move freely with the tape roller bearing cylindrical peripheral surface in a direction perpendicular to the central axis, and constraining movement of the tape in the lateral direction. The frictional surface limits slip in the lateral direction, thereby reducing the rate of the lateral transient movement of the tape to allow the track following servo system to follow the reduced rate lateral transient movement of the longitudinal tracks.

Thus, the tape is contacted and engaged at its surface rather than at an edge, constraining the tape in the lateral direction, providing substantial lateral drag to the tape, such that the tape is able to move laterally at a slower rate as the tape roller bearing rotates, which can substantially reduce the rate of the lateral transient movement. The grooved tape engagement surface substantially quenches any potential air bearing that could form between the surface of the tape and the surface of the roller bearing, e.g., due to the air drawn along by the tape as it is moved rapidly. As a result, an air bearing beginning to form is generally collapsed to ensure that the roller bearing frictionally contacts and engages the surface of the tape. A flat cylindrical surface may also be provided at the edges of the tape to fully support the tape edges.

Another approach has been to provide rollers having a crowned tape engagement surface which exerts a lateral force on the tape which tends to restore the tape to a central position. However, the effectiveness of this approach can be limited due to various factors such as the Young\'s Modulus exhibited by the tape and the degree of strain permitted to be exerted on the tape.

Yet another approach utilizes a post having a concave tape engagement surface rather than a crowned tape engagement surface. Here too, the curvature can provide some restoring force to center the tape. However, like the crowned tape engagement surface, the concave curvature is limited by the allowable tension gradient in the tape. Typically, the tension gradient is maximum when the tape is at nominal tension and the edges are “baggy” or at zero tension.

It has also been proposed to use sensors to detect the lateral position of the tape edge as it passes the bearing and to tilt the bearing in an active closed control loop to control the lateral position of the tape. It is recognized that tilting the bearing can introduce a gradient of tension between the top and bottom edges of tape which can be used to actively steer the tape riding on an air bearing formed between the tape and the physical bearing surface. However, the air bearing may be inadvertently quenched such as when the tape stops or momentary stiction occurs between the tape and the physical bearing surface. As a consequence, a momentary loss of control of the tape may be produced which may have severe consequences causing damage to the tape.

SUMMARY

A tape movement constraint is provided for a tape drive system. In one embodiment, a roller barrel of a tiltable roller bearing is biased in a first position on a pivot axis relative to a base support frame, using magnetic attraction between a movable magnet and a return path structure of magnetically permeable material. The roller barrel is pivoted on the pivot axis relative to the base support frame by conducting current through a fixed coil to generate a magnetic field which is conducted by the return path structure to interact with the magnetic field of the magnet. The roller barrel pivots on the pivot axis as a function of the magnitude and direction of the current through the coil.

In the illustrated embodiment, the tiltable tape roller bearing of the constraint system is positioned along the tape path closely adjacent the tape head, has a cylindrical peripheral surface parallel to the lateral direction of the tape and extending a length greater than the width of the tape, for contacting a surface of the tape. The tape roller bearing is rotatable about a central axis parallel to the cylindrical peripheral surface, allowing the tape freedom of movement in the longitudinal direction.

The tiltable cylindrical peripheral surface comprises a frictional surface for contacting and engaging the surface of the tape, allowing the tape to move freely with the tape roller bearing cylindrical peripheral surface in a direction perpendicular to the central axis, and constraining movement of the tape in the lateral direction. The frictional surface limits slip in the lateral direction, thereby reducing the rate of the lateral transient movement of the tape to allow the track following servo system to follow the reduced rate lateral transient movement of the longitudinal tracks.

Thus, the tape is contacted and engaged at its surface rather than at an edge, constraining the tape in the lateral direction, providing substantial lateral drag to the tape, such that the tape is able to move laterally at a slower rate as the tape roller bearing rotates, substantially reducing the rate of the lateral transient movement. In one embodiment, any potential air bearing that could form between the surface of the tape and the surface of the roller bearing, e.g., due to the air drawn along by the tape as it is moved rapidly, is collapsed to insure that the roller bearing frictionally contacts and engages the surface of the tape.

The tape drive system moves the tape along a tape path in a longitudinal direction across a tape head, the tape having tracks extending in the longitudinal direction, the tape head having a track following servo system for moving the head in a lateral direction for following lateral movement of the longitudinal tracks, where the tape is subject to lateral transient movement.

Other embodiments are described and claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the present description, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.

FIG. 1 is a partially cut away perspective view of a tape drive in accordance with one embodiment of the present description;

FIG. 2 is an isometric view, illustrating one embodiment of a tiltable roller bearing in accordance with the present description, which may be employed in the tape drive of FIG. 1;

FIG. 3a is a side schematic diagram of an embodiment of a constraint system in accordance with the present description, which may be employed in the tape drive of FIG. 1;

FIG. 3b is a top, schematic view of one embodiment of the interaction of permanent magnets and a magnetic return path structure in an actuator of a tiltable roller bearing in accordance with the present description;

FIG. 4a is an isometric view, illustrating an embodiment of a tiltable roller bearing of the constraint system illustrated in FIG. 3a, in accordance with the present description, which may be employed in the tape drive of FIG. 1;

FIG. 4b is an isometric view, illustrating the tiltable roller bearing of FIG. 4a, depicted with the roller barrel omitted for clarity;

FIG. 5a is an isometric view, illustrating one embodiment of an actuator for the tiltable roller bearing of FIG. 4a;

FIG. 5b is an isometric view, illustrating the actuator of FIG. 5a with a second support structure which includes a magnet holder;

FIG. 5c is an isometric view, illustrating the actuator and second support structure of FIG. 5b, with the coil omitted for clarity;

FIG. 6a is an isometric view, illustrating the second support structure of FIG. 5c together with the magnets of the actuator;

FIG. 6b is a front view, illustrating the second support structure of FIG. 5c together with the magnets of the actuator;

FIG. 6c is a side view, illustrating the second support structure of FIG. 5c together with the magnets of the actuator, in a first, untilted position with respect to the roller barrel and magnetic return path structure which are shown in phantom;

FIG. 6d is a side view, illustrating the second support structure of FIG. 5c together with the magnets of the actuator, in a second, tilted position with respect to the roller barrel and magnetic return path structure which are shown in phantom;

FIG. 7 is a flowchart depicting one example of operations of the tape constraint system of FIG. 3a, in accordance with the present description;

FIGS. 8a and 8b depict a simulation of one example of dynamics of operations of the tape constraint system of FIG. 3a, in accordance with the present description;

FIGS. 9a and 9b are enlarged views of alternative embodiments of the roller bearing barrel of FIG. 2;

FIGS. 10-13 are enlarged views of alternative embodiments of the roller bearing barrel of FIG. 2; and

FIGS. 14a and 14b are diagrammatic representations of alternative embodiments of peripheral surfaces of the roller bearing barrel of FIG. 2 in accordance with the present description.

DETAILED DESCRIPTION

In the following description with reference to the Figures, like numbers represent the same or similar elements. It will be appreciated by those skilled in the art that variations may be accomplished in view of these teachings without deviating from the spirit or scope of the present description.

Referring to FIG. 1, a tape drive 10, such as a magnetic tape drive, in accordance with one aspect of the present description, is illustrated. A magnetic tape 11 is moved along a tape path from a supply reel 12 in a magnetic cartridge 13 to a take up reel 14, the reels comprising drive reels of a drive system operated by drive motors. The magnetic tape is moved along the tape path in a longitudinal direction across a tape head 15. The tape head is supported by an actuator 17 of a servo system, which, for example, may comprise a compound actuator. The tape head 15, for example, a magnetic tape head, may comprise a plurality of read and write elements and a plurality of servo read elements. The tape may comprise a plurality of servo tracks or bands 18 which are recorded on the tape in the longitudinal direction on the tape and are parallel to the data tracks. The servo read elements are part of a track following servo system for moving the tape head 15 in a lateral direction for following lateral movement of the longitudinal tracks as the tape 11 is moved in the longitudinal direction, and thereby position the tape head at the data tracks and follow the data tracks.

The compound actuator may comprise a coarse actuator, such as a stepper motor, and a fine actuator, such as a voice coil, mounted on the coarse actuator. The fine actuator in this embodiment has a high bandwidth for a very limited lateral movement, called “fine” track following, for allowing the tape head to accurately follow small displacements of the tape. Larger movement of the tape head is in this embodiment conducted by the coarse actuator for centering the actuator at the average position of the fine actuator during track following, and is also employed to shift the tape head from one set of tracks to another set, and is conducted at a slow rate. An example of a compound actuator is described in coassigned U.S. Pat. No. 5,793,573. It is appreciated that many differing types of actuators may be employed in embodiments of the present description, depending upon the particular application.

The tape drive 10 additionally comprises a controller 20 which provides the electronics modules and processor to implement a servo system to operate the compound actuator. In addition, the controller 20 provides the electronics modules and processor portion of the tape movement constraint described below.

The magnetic tape 11 of the present example may be provided in a tape cartridge or cassette 13 having a supply reel 12 or having both the supply and take up reels. The servo tracks or bands 18 may comprise any of several types of longitudinal servo patterns as is known to those of skill in the art. For example, a timing based servo pattern is described in coassigned U.S. Pat. No. 5,689,384, and comprises magnetic transitions recorded at more than one azimuthal orientation across the width of the servo track. In one example, five longitudinal timing based servo tracks are prerecorded on the magnetic tape for track following at these positions. The pattern of magnetic transitions recorded in the servo tracks is a repeated set of frames, each of which are of different azimuthal orientations. Thus, the tape head 15 may comprise at least two narrow servo read elements allowing two servo tracks to be sensed simultaneously, and the outputs used redundantly to reduce error rates.

In this example, the magnetic tape 11 may also be provided with suitable guard bands at the edges of the tape, and four data track regions between the servo tracks.

A plurality of read and write elements may be provided at the tape head 15 for reading and/or writing data on the tape 11. When the servo elements are properly positioned at the specific servo tracks, the read and write elements are properly positioned to transfer data with respect to the corresponding data track locations of the tape 11.



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Magnetically biased tilting roller bearing tape guidance
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stats Patent Info
Application #
US 20130021693 A1
Publish Date
01/24/2013
Document #
13555833
File Date
07/23/2012
USPTO Class
360 7304
Other USPTO Classes
G9B 15054
International Class
11B15/46
Drawings
8


Magnetic Field


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